In addition to measuring the elevation of the surface of the ground, surveyors site the elevation of underground fixtures such as sewer pipes and the like. A sewer system comprises a plurality of underground pipes for transporting water and sewage from one portion of a municipality to another and surveyors are called upon to site the elevation of those pipes. An underground sewer system typically has a plurality of union boxes to which underground pipes connect, and the union boxes are accessible through manholes, which typically open to a street overhead.
To site the elevation of a pipe entering into a union box positioned below a manhole, a surveyor must extend an elongate member having dimensions thereon into the manhole until the end of the elongate member makes contact with the portion of the pipe the elevation of which is desired. Thereafter, the surveyor must determine the length of the portion of the elongate member that extends into the manhole. This may be done by reading dimensions printed along the elongate member at a known elevation, for example, the elevation of the upper edge of the manhole, or by placing a mark on the pole and measuring the distance from the mark to the end of the pole. The surveyor must also factor in the angle at which the elongate member extends through the manhole. Once the length of the elongate member extending into the manhole and the angle of incline are known, the elevation of the lower end of the elongate member can be calculated using simple trigonometry.
The tools needed to measure the elevation of a pipe connecting into a union box are the elongated member with dimensions along the length thereof, and a device for determining the angle of incline of the member. It may also be desirable to provide a second elongate member to extend across the upper surface of a manhole for providing a marker to be read against the dimensions of the elongate member to simplify the reading of the length extending into the manhole. A device for measuring the incline of the elongate member is also needed.
Although the process appears simple, as a practical matter surveyors have great difficulty in accurately measuring the elevation of pipes that connect into union boxes accessible only through a manhole. First, the end of the elongate member, typically a range pole or a level rod, must be maintained in contact with the pipe while the measurements are being made. Second, it is difficult to properly determine the portion of the length of the elongate member extending into the manhole. And third, it is difficult to determine the angle of inclination of the elongate member while the distal end thereof remains in contact with the portion of the pipe, the elevation of which is desired. The parts tend to move with respect to one another. Also, the reading of the angle of the elongate member may not measure the maximum angle of inclination unless the angle is measured from a plumb. The consequences will be that the final calculation of the elevation of the pipe will be incorrect.
There are numerous devices intended to solve the forgoing problem, but as a practical matter the parts that make up the devices of the prior art are difficult to store and carry and are therefore generally not in current use by surveyors. It would be desirable therefore, to provide an improved device for measuring the elevation of a pipe entering a union box below a manhole.